GB1280739A - Improvements in or relating to distance protective systems for intermeshed electrical networks - Google Patents

Abstract

1280739 Protective arrangements SPRECHER & SCHUH AG 4 Nov 1970 [21 Nov 1969] 52344/70 Heading H2K A system for protecting a network in which a fault 18 may be fed from more than one point 3, 4, comprises multi-zone directional impedance relays 14 ... 17 associated with circuit-breakers 9 ... 12 in respective feeders 5, 6, and a central computer 19 connected by transmission lines 20, 21 to all the circuit breakers and relays for adjusting the settings of the relays in their second and third zones of protection in dependence on the states of the various circuit-breakers. Thus with a fault at 18 supplied only from generator 3, relay 14 would function normally with a time delay appropriate to its second or third zone operation should the relay 16 fail to operate. With a fault at 18 supplied from both generators 2, 3, the relay 14 can function at an apparent higher impedance as, in response to the closing of the circuit-breaker 13, the computer 19 will have changed the settings of the various relays for their second and third zone operation. Each relay may have a current transformer 23 connected to a replica impedance 25, 26, a voltage transformer 22 connected to resistors 27, 28, 29 which determine the three zones, a measuring device 30 with polarizing supply 31, an overourrent starter relay 32 controlling time delay relays 33, 34 which change the tappings to the resistors to select the zone of protection, and relays 34<SP>1</SP>, 35 controlled by the computer.